Conventional electric fuel pumps have an electric motor mounted next to the pumping unit and share a common drive shaft. The motor brushes are located at the far end of the unit, opposite the pumping unit. Where an electric fuel pump size reduction is to be had, to reduce its overall size, the electric motor brush structure suffers an intensified size reduction affecting its efficiency and longevity. Since the shaft and rotor have to be of sufficient size to develop the torque to drive the electric motor, their size approaches a lower limit. Generally the exterior most portion of the brushes suffer the same separation restriction in order to stay no more than flush with the external portion of the electric motor body. Brushes which must operate within a restricted lower limit size have very little operating room and are forced to be quite small in terms of both length and cross-sectional area. The size of the brushes are related to the arc width of the contacts on the armature. A larger diameter of armature contact assembly would provide for brushes of larger cross sectional area, but the length of the brush bore which supports the contact force spring, brush and electrical contact has a minimum length requirement, and must reside in the radial space which includes spacing for the commutator, brushes and their wear length, springs and their length of urging force contact ability over the wear length, and the electrical contacts used to connect conductors to the brushes.
Another limitation and condition is thermal waste heat. The arcing and eddy currents which occur at the commutator is significant. Where the commutator area is open, as with most motors, sufficient ventilation occurs. However, in a hydrocarbon environment exposure and ventilation could easily spark a fire or explosion. Consequently, electrical "explosion proof" standards and structure are employed at the brush end of a motor in order to try to provide ventilation for cooling and at the same time limit availability of the open spark to flammable hydrocarbons. This usually requires a heavy set of baffles which enable ventilation but which will suppress ignition.
Another problem involves the stability of the connection between the motor and pump. For cheaper pumps, the strength of the shaft is significantly relied upon to give rigidity of the pump and motor combination. It would be desirable for the pump and motor combination to be more highly integrated so that less reliance would be had on the shaft strength in forming an integrated unit.
What is therefore needed is a truly integrated pump and motor combination which will allow larger cross section brushes, more room for the brushes to move and wear, which all but eliminates the sparking ability of the commutator to cause fires, but without all of the extra structure and requirements to permit ventilation simultaneous with cooling, and which enables ease of mounting in different positions.